Cordless products or devices which use rechargeable batteries are prevalent in the marketplace. Rechargeable batteries may be used in numerous devices ranging from computers to power tools. Since the devices use a plurality of battery cells, the battery cells are commonly packaged in a battery pack. The battery pack may in turn be used to power the devices when coupled thereto. Once depleted, the battery pack may be recharged by a battery charger.
Over the past few years, lithium-ion (Li-ion) batteries have begun replacing nickel-cadmium (NiCd), nickel-metal-hydride (NiMH), and lead-acid batteries in such portable electronic devices. As compared to NiCd and NiMH batteries, Li-ion batteries are lighter but have a larger capacity per unit volume. For this reason, the Li-ion batteries are suitable to devices that are preferably light and which are required to endure continuous use for a long time. Li-ion batteries, however, may deteriorate rapidly when subjected to overcharging, over-discharging, overheating, or other adverse conditions. Therefore, these types of devices employ protective measures to prevent such adverse conditions. Upon detecting an adverse condition, the system can be designed to abruptly terminate discharge of current from the batteries and thereby cease device operation.
Therefore, it is desirable to develop a protection scheme that prolongs operation of the device before current discharge is terminated and/or warn the operator that the device is approaching a condition which requires terminating current discharge. This section provides background information related to the present disclosure which is not necessarily prior art.